<div class="container">

    <form class="form-signin">
        <h2 class="form-signin-heading">请登录</h2>
        <label for="inputEmail" class="sr-only">用户名</label>
        <input type="email" id="inputEmail" class="form-control" placeholder="Email address" required autofocus>
        <label for="inputPassword" class="sr-only">密码</label>
        <input type="password" id="inputPassword" class="form-control" placeholder="Password" required>
        <hr>
        <button class="btn btn-lg btn-primary btn-block" type="submit">Sign in</button>
    </form>

</div> <!-- /container -->